Log Message:
libebml: updated to 1.3.6

v1.3.6.
* Converted the build system from autoconf/automake to
cmake. Patches by Github user "evpobr" with fixes by myself.
* Fixed undefined behavior when reading signed integers with
negative values from files (though compilers implemented this the
way we wanted them to already).
* Fixed a small memory leak when reading an element runs into an
I/O exception (e.g. due to having reached the end of the file).
* Fixed the EbmlMaster::GetDataStart() function returning wrong
values for elements with an infinite/unknown size.
* Fixed finding the next element ID when garbage data is
encountered during the scan for the ID.
* Fixed several potential situations where reading child element
data could exceed the parent element's size.
* Added a code of conduct to the project.